1. Field of Invention
The invention relates to near field communications (NFC), and more specifically to tuning an antenna of a NFC device.
2. Related Art
Near field communication (NFC) devices are being integrated into communication devices, such as mobile devices to provide an example, to facilitate the use of these communication devices in conducting daily transactions and facilitate cordless power transfer. For example, instead of carrying numerous credit cards, the credit information provided by these credit cards could be stored onto a NFC device. The NFC device is simply tapped to a credit card terminal to relay the credit information to it to complete a transaction. As another example, a ticketing writing system, such as those used in bus and train terminals, may simply write ticket fare information onto the NFC device instead of providing a ticket to a passenger. The passenger simply taps the NFC device to a reader to ride the bus or the train without the use of a paper ticket.
Generally, NFC requires that NFC devices to be present within a relatively small distance from one another so that their corresponding magnetic fields can exchange information and transfer power. Typically, a first NFC device transmits or generates a magnetic field modulated with the information or requests for information, such as the credit information or the ticket fare information. This magnetic field inductively couples the information and power onto a second NFC device that is proximate to the first NFC device. The first NFC device conventionally uses amplitude modulation (AM) and/or phase modulation (PM) of the radio frequency (RF) field that it transmits or generates. The second NFC device may respond to the first NFC device by inductively coupling its corresponding information onto the first NFC device where the second NFC device modifies the load that it presents to the RF magnetic field.
Conventionally, the information is modulated onto a carrier frequency of 13.56 MHz. The first NFC device and the second NFC device each include an antenna system that is ideally tuned to a specific frequency. The first NFC device acting as the reader is tuned to 13.56 MHz while the second NFC device acting as a passive tag is tuned to a higher frequency. The antenna systems may include a series resonant LC antenna circuit and/or a parallel resonant LC circuit. For example, the first NFC device may use the series resonant LC antenna circuit, while the second NFC device may use the parallel resonant LC circuit. However, components that are used to implement these antenna systems may be affected by the manufacturing tolerances which cause their actual values to differ from their expected values. As a result, the antenna system may be actually tuned to a different resonant frequency than expected.
Conventionally, the antenna systems that are designed to be tuned and/or also antenna systems that are not designed to be tuned, may have improved performance by selecting appropriate external components, to compensate for the manufacturing tolerances. The use of high precision components and/or resonant network trimming in production may mitigate against the effects of variations in manufacturing tolerances but at an increased cost and an increase in the complexity of the NFC device. Manual and/or machine trimming may also be used to mitigate against the effects of variations in manufacturing tolerances but further increasing the cost and complexity of the NFC device.
Thus, there is a need for a way to tune a NFC device so that such tuning is effective but inexpensive in the manufacturing of NFC devices. Further aspects and advantages of the invention will become apparent from the detailed description that follows.
The invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.